BACKGROUND: Metabolic syndrome (MSY) is associated with an increased risk of cardiovascular disease, type 2 diabetes, and recurrence in breast cancer survivors (BCS). MSY is 1.5 times more common in Hispanic women compared with non-Hispanic women. Although exercise mitigates MSY in BCS, to the best of the authors' knowledge, few studies to date have focused on minorities. This secondary analysis examined ethnicity as a moderator of the effects of a 16-week aerobic and resistance exercise intervention on MSY, sarcopenic obesity, and serum biomarkers in BCS. METHODS: A total of 100 eligible BCS were randomized to exercise (50 BCS) or usual care (50 BCS). The exercise intervention promoted moderate to vigorous aerobic and resistance exercise 3 times a week for 16 weeks. MSY z scores, sarcopenic obesity, and serum biomarkers were measured at baseline, after the intervention, and at the 28-week follow-up (exercise group only). Linear mixed models adjusted for baseline values of the outcome, age, disease stage, adjuvant treatment, and recent physical activity were used to evaluate effect modification by ethnicity. RESULTS: The study sample was 57% Hispanic BCS (HBCS) and 43% non-Hispanic BCS (NHBCS). HBCS were younger, of greater adiposity, and had been diagnosed with more advanced cancers compared with NHBCS (P<.001). Ethnicity was found to moderate the mean differences in exercise training on triglycerides (-36.4 mg/dL; 95% confidence interval [95% CI],-64.1 to -18.8 mg/dL), glucose (-8.6 mg/dL; 95% CI, -19.1 to -3.0 mg/dL), and C-reactive protein (-3.3 mg/L; 95% CI, -7.3 to -0.9 mg/L). CONCLUSIONS: HBCS appear to have poorer metabolic profiles and therefore may derive relatively larger metabolic changes from exercise compared with NHBCS. Clinical exercise interventions may attenuate existing health disparities across diverse groups of BCS.